1. Field of the Invention
The invention relates to a moving magnet-type actuator for converting electrical energy into reciprocating kinetic energy or the like by electromagnetic action for use in control equipments, electronic equipments, machine tools and the like.
2. Description of the Related Art
Conventionally, moving magnet-type reciprocating devices have a structure such as shown in a first conventional example of FIG. 1 and a structure such as shown in a second conventional example of FIG. 2.
In the first conventional example shown in FIG. 1, reference numeral 10 designates a magnet moving body made of a bar-shaped permanent magnet magnetized in the axial direction. This bar magnet moving body has magnetic poles at both ends thereof. Coils 11A, 11B are wound around annularly the outer circumferences of both end portions of the magnet moving body 10 in such a manner that the same poles are generated at neighboring portions thereof. Although not shown in FIG. 1, the coils 11A, 11B are usually installed into a nonmagnetic guide sleeve member for movably guiding the magnet moving body 10 in the axial direction. Magnetic flux from the respective end surfaces of the magnet moving body 10 links with the respective coils 11A, 11B.
In the second conventional example shown in FIG. 2, a magnet moving body 15 is formed by firmly integrating two bar-shaped permanent magnets 16A and 16B with a bar-shaped magnetic substance 17 in such a manner that the same poles of the permanent magnets confront each other and that the magnetic substance is interposed between the permanent magnets. A coil 18 is wound annularly around the outer circumference of the middle portion of the magnet moving body 15. Although not shown in FIG. 2, the coil 18 is usually installed into a nonmagnetic guide sleeve member for movably guiding the magnet moving body 15 in the axial direction. Magnetic flux from the end surfaces of the permanent magnets with the same poles thereof confronting each other in the magnet moving body 15 links with the coil 18.
As the second conventional example shown in FIG. 2, the magnet moving body in which same poles of magnets are confronting each other is disclosed in U.S. Pat. No. 4,363,980.
By the way, in the first and second conventional examples, a force to be generated at the magnet moving bodies 10 or 15 is produced based on the Fieming's left hand rule. The Fieming's left hand rule is applied to coils. Since the coils are fixed in the above cases, a thrust is produced at the magnet moving body as reaction against force acting on the coils. Therefore, what contributes to producing a thrust is a vertical component of the magnetic flux from the permanent magnets of the magnet moving body (the component perpendicular to the direction of magnetization of the permanent magnets).
How the vertical component of the magnetic flux behaves was analyzed in two cases: a case where only one permanent magnet was used and a case where two permanent magnets arranged so that the same poles confront each other were used.
FIG. 3 shows a result obtained from a magnetic field analysis of the vertical component of the surface magnetic flux density made along with the longitudinal side surface of a single permanent magnet. The permanent magnet used in the analysis was a rare-earth permanent magnet whose diameter was 2.5 mm and whose length was 6 mm. Measurements were made at positions 0.25 to 0.45 mm distant from the surface of the permanent magnet.
FIGS. 4 to 7 show results obtained from magnetic field analysis of the vertical component of the surface magnetic flux density made along the longitudinal side surface of two permanent magnets in the cases where the two permanent magnets are arranged so that the same poles thereof confront each other with confronting gaps of 0, 1, 2, 3 mm, respectively. Each of the permanent magnets used was a rare-earth permanent magnet whose diameter was 2.5 mm and whose length was 3 mm. Measurements were made at positions 0.25 to 0.45 mm distant from the surface of the permanent magnets.
FIG. 8 shows a result obtained from a magnetic field analysis of the vertical component of the surface magnetic flux density made along the longitudinal side surface of two permanent magnets in a case where the two permanent magnets are arranged so that the same poles thereof confront each other while interposing a 1 mm-long magnetic substance therebetween. Each of the permanent magnets used was a rare-earth permanent magnet whose diameter was 2.5 mm and whose length was 3 mm. Measurements were made at positions 0.25 to 0.45 mm distant from the surface of the permanent magnets.
As described above, the force produced at the magnet moving body is based on the Fieming's left hand rule, and it is desired that the vertical component of the magnetic flux of the permanent magnets which cuts across the coils (the component perpendicular to the axial direction of the permanent magnets) be large in quantity. However, in the first conventional example shown in FIG. 1, the vertical component of the surface magnetic flux density is as shown in FIG. 3, verifying that the vertical component in the first conventional example was smaller compared with the cases where the two permanent magnets were arranged with the same poles thereof confronting each other such as shown in FIGS. 4 to 8. Therefore, it is limited the improvement of the thrust by the configuration of the first conventional example shown in FIG. 1. For example, a force F1 of only 4.7 (gf) was produced under the condition that the magnet moving body 10 was formed of a rare-earth permanent magnet of 2.5 mm in diameter and 6 mm in length and that a current of 40 mA was applied to the two coils 11A, 11B so that the same poles can be generated at the neighboring portions of the coils 11A, 11B.
On the other hand, in the second conventional example of FIG. 1, the magnet moving body 15 interposing the magnetic substance between the two permanent magnets with the same poles thereof confronting each other was used. The vertical component of the magnetic flux density in the second conventional example is as shown in FIG. 8, which indicates that the magnetic flux produced from the magnetic poles of the permanent magnets 16A and 16B arranged so that the same poles thereof confront each other was larger than in the case of a single permanent magnet (see FIG. 3) or of only two permanent magnets (see FIGS. 4 to 7). However, it is only one coil that was involved in this configuration that surrounds the middle portion of the magnet moving body 15, and this configuration seems to leave the magnetic flux produced from the magnetic poles at both ends of the magnet moving body 15 not utilized effectively. It was thus difficult to improve thrust also in the second conventional example of FIG. 2. For example, in the second conventional example of FIG. 2, a force F2 of only 5.6 (gf) was produced when the same power consumption as in the first conventional example was achieved under the condition that a current of 40 mA was applied to the coil 18 while using a magnet moving body that Was formed by interposing a 1 mm-long magnetic substance between two rare-earth permanent magnets as the magnet moving body 15. The coil 18 was prepared so that the same power consumption as in the first conventional example of FIG. 6 could be obtained. Each of the two permanent magnets was 2.5 mm in diameter and 3 mm in length (the performance of the rare-earth permanent magnet was the same as that of the first conventional example).
If the magnet moving body is formed by combining a plurality of permanent magnets and magnetic substances, then these components must be unified with one another surely. Further, if the actuator is formed by arranging an output extracting pin or pins on the permanent magnets, it is desirable to eliminate unnecessary play of the magnet moving body and the output extracting pins. This point must therefore be taken into consideration.